1. Field of the Invention
The present invention relates to a method and system for monitoring the deformations of a tyre in motion.
In particular, the present invention relates to the possibility of determining the deformations of the carcass structure of a tire from inside it, for example in order to provide automatic intervention actuated or commanded by the driver, in the driving and/or control system of the vehicle, to change the vehicle""s behaviour according to measurements made on the tyre.
2. Description of the Relevant
There are known prior art devices for measuring characteristic parameters such as pressure and temperature inside a tyre.
Patent application EP 887211 describes a tyre monitoring system comprising a sensor which is positioned inside the tyre and is enabled to create an electrical impulse when the said sensor passes through the footprint area formed by the contact of the tyre with the ground during rolling. The system described in this patent also comprises means for finding the ratio of the said electrical impulse to the duration of one revolution of the tyre and means for transmitting the said ratio to a processing unit within the vehicle.
In particular, the sensor is placed within the tread of the tyre in such a way that the said electrical impulse has a first peak at the entry of the sensor into the footprint area and a second peak at the exit from the footprint area.
According to the teaching of this patent, the ratio between the time elapsed between the two peaks and the period of a complete revolution makes it possible to know the flattening of the tyre during the travel of the vehicle.
This is because the sensor determines the instant of entry into the footprint area and the instant of exit from said area. It is thus possible to measure the length of this area, if the angular velocity of the tyre and its radius are known. The length of the footprint area is then related to the flattening of the tyre, which is a critical parameter of the tyre in operation, particularly in tyres for heavy motor transport.
Patent application EP 689950 describes a different method for determining parameters of a tyre such as its pressure and temperature. In particular, a self-powered programmable electronic device positioned on the inner surface of a tyre or on its mounting rim is used. This device can be used to determine and store the pressure, temperature and the number of rotations of the tyre, and may comprise an extensometer whose output signal measures the bending of the inner surface of the tread, or an accelerometer which measures the value of the acceleration which the tread undergoes. Additionally, the device is activated by an external radio-frequency signal and transmits an alarm signal if a predetermined limit of the measured values is exceeded.
There are also known methods for measuring deformations of the tread of a tyre during motion and for transmitting it to a receiver located on the vehicle.
Patent application WO 9325400 describes a sensor, comprising a resonant circuit which oscillates at a predetermined characteristic frequency, is located within the tread of a tyre, and is capable of transmitting a signal directly dependent on the aforesaid deformations. This resonant frequency is affected by the deformations of the tread during motion and the sensor transmits electromagnetic waves proportional to these variations of the resonant frequency. These electromagnetic waves are received by a processing unit connected to a receiver located inside the vehicle.
U.S. Pat. No. 5,247,831 describes a method for monitoring the behaviour of the footprint area of a tyre during the travel of the vehicle, in order to optimize the driving of the vehicle. In particular, a piezoelectric sensor consisting of longitudinal strips of piezoresistive rubber is inserted into the tread. This sensor is capable of measuring the deformations of the tread, since the strips change their electrical resistance as a function of the said deformations.
There are also known methods and devices for acting on the driving and/or control system of the vehicle, particularly on the devices which control the suspension of the vehicle, to control its behaviour according to the information obtained from the axles of the vehicle or from the wheel hubs.
The publication xe2x80x9cA method for the evaluation of the lateral stability of vehicles and tyresxe2x80x9d by the Societa Pneumatici Pirelli S.p.A., presented at the International Automobile Tire Conference, Toronto, Canada, on Oct. 22, 1974, illustrated a method for determining the dynamic behaviour of the vehicle as a function of the forces developed by the various types of tyre sets and the various conditions of the road surface.
The publication principally cites three forces which determine the dynamic behaviour of a tyre, namely the vertical force, the longitudinal force and the lateral force.
The vertical force is that which is due to the dynamic load to which the tyre is subjected. The longitudinal force is that which is due to the moment applied to the axis of the tyre as a result of an acceleration or braking of the vehicle. The lateral force, also present in conditions of normal travel in rectilinear motion, is the resultant of the force due to the characteristic angles of the vehicle suspension (camber and toe-in) and to the ply-steer developed by the layers of inclined cords of the belt structure of the tyre, and of the thrust generated by the centrifugal force during drifting. The sum of the forces developed by the four tyres generates a resultant system applied to the centre of gravity of the vehicle, which balances the inertial forces and determines the attitude of the vehicle as a function of the characteristics of the suspension system of each axle. This resultant system is determined by means of suitable accelerometers, one positioned on the front axle and one on the rear axle of the vehicle. The article shows a set of graphs showing the centripetal acceleration or the centripetal force applied to the centre of gravity of the vehicle as a function of the angle of slip of the corresponding axle. From graphs plotted for different ground conditions and different types of tyres, it is possible to determine the behaviour of the vehicle provided with a predetermined set of tyres and to determine any lateral slipping of either the front or the rear axle in cornering.
The Applicant has observed that the aforesaid known systems of controlling the behaviour of the vehicle are based on systems of forces measured at the hubs of the wheels, and the systems of measuring the deformations of the tyre are based on the determination of the deformations undergone by the tread in the footprint area of the tyre.
The Applicant has observed that the values measured in these systems cannot be related in a biunique way to the conditions of travel of the tyre and, more precisely, to the system of forces developed by the tyre in each condition of travel.
The present invention is based on the Applicant""s perception that the determination of deformations of the tread, particularly in the footprint area of the tyre, does not make it possible to identify the system of forces developed by the tyre or the deformations of the tyre carcass which are associated with it and which represent the behaviour of the tyre. This behaviour is of considerable importance, especially during certain particular events, such as the braking or acceleration of the vehicle, drifting, and variations of load on the tyre.
According to the above, the present invention originated from the Applicant""s perception that the determination of the deformations of the tyre carcass, which are related in a biunique way to the system of forces developed by the tyre in operation, makes it possible to determine the behaviour of the tyre in any of its conditions of motion.
It has been found that the measurements of the deformation of the carcass structure of the tyre, at a given inflation pressure, according to a set of three Cartesian axes, in other words the deformation in the vertical direction, the deformation in the transverse direction and the deformation in the longitudinal direction, correspond in a biunique way, or in any case a reproducible way, to the vertical, lateral and longitudinal forces respectively which act on the tyre (or, in other words, to the forces which the tyre exchanges with the ground).
The Applicant has previously described this technical solution and the determinations associated with it in patent application 99EP-114962.6, to which reference should be made for further and more detailed information, and which is to be understood as being integrally incorporated in this description.
The Applicant has previously described a particular method and a particular type of device for making the aforesaid determinations in patent application 99EP-125692.6. In this patent application, these deformations are determined by means of a sensor which measures the distance between the sensor itself and certain predetermined points on the inner surface of the tyre liner. The size of the deformations of the carcassstructure of the tyre can be deduced from these distances by means of a calculation.
The present invention relates more specifically to a further method and a further type of device for carrying out the aforesaid determinations.
In particular, the Applicant has discovered a method for determining the deformations of a tyre in motion, which consists in measuring these characteristic values within the tyre by means of a single sensor which illuminates the inner surface of the tyre liner. Areas of high light reflection and areas of low light reflection are formed adjacent to each other on the inner surface of the liner. From the points of discontinuity formed between an area of high light reflection and an area of low light reflection, this sensor determines the deformation of the tyre in the lateral direction, in the longitudinal direction and in the vertical direction. The determination is preferably carried out when the areas of the inner surface which have this alternation of illuminated areas and dark areas are within the footprint area of the tyre.
In a first aspect, the present invention relates to a system for monitoring the deformations of a moving tyre fitted on a rim associated with a vehicle, characterized in that it comprises:
a moving station located in a predetermined position on the said rim and capable of sending an optical beam towards the inner surface of the tyre, receiving the light reflected from the said surface and emitting a signal proportional to the deformations of the tyre in a longitudinal direction, in a transverse direction, and in a vertical direction,
a reflecting element positioned on the said inner surface of the tyre, comprising a region which has at least one area of high light reflection and one area of low light reflection, and which is capable of reflecting the said optical beam.
The said system also comprises a fixed station positioned on the said vehicle and capable of receiving the said signal from the said moving station.
Preferably, the said area of high light reflection is produced by colouring the inner surface of the tyre with a reflective paint.
In particular, the said region comprises a plurality of triangles adjacent to each other.
Preferably, the said fixed station is capable of enabling the said measurement carried out by the said moving station.
In particular, the said moving station comprises at least one sensor and an electronic circuit board with which are associated an optical beam emitting device, a first lens, an optical beam receiving device and a second lens.
In particular, the said fixed station comprises a supporting element, fixed at one of its ends to a hub on which the said rim is mounted, and an electronic circuit board fixed to the said supporting element.
In particular, the said electronic circuit board of the fixed station comprises an oscillator circuit which supplies a drive circuit for a first antenna, a radio-frequency receiver connected to the said first antenna, and an electrical demodulator device connected to the said radio-frequency receiver.
Preferably, the fixed station is powered by the battery of the vehicle on which the tyre is fitted.
In particular, the said electronic circuit board of the sensor comprises a second antenna, connected to a power supply unit, which supplies a drive circuit for the said optical beam emitter and a drive circuit for the said optical beam receiver, and a circuit for reading the electrical signal emitted by the said optical beam receiver.
Preferably, the said optical beam emitter comprises an LED or a laser diode.
Preferably, the said optical beam receiver comprises at least one CCD element or a CMOS element.
In a second aspect, the present invention relates to a method for monitoring the deformations of a moving tyre fitted on a rim associated with a vehicle, characterized in that it comprises the following steps:
emitting a signal within the tyre from a predetermined position on the said rim,
reflecting this signal from the inner surface of the tyre,
receiving this reflected signal,
processing the received signal in such a way as to generate a signal proportional to the deformations of the tyre in a longitudinal direction, in a transverse direction and in a vertical direction.
In particular, the said step of emitting a signal comprises:
enabling a moving station located on the said rim to emit the said signal when the said moving station passes through the footprint area of the tyre.
Additionally, the said method also comprises the step of transferring the said signal processed by the said moving station to a fixed station located on the said vehicle.
Preferably, the said step of enabling a moving station is carried out by the said fixed station.
In particular, the said step of enabling the moving station comprises supplying power to the moving station for a time interval during which the step of transferring the processed signal from the said moving station to the said fixed station is also carried out.
In particular, the said step of enabling a moving station comprises generating a magnetic field at the said fixed station in the direction of the said moving station and of supplying power by means of the said magnetic field to a drive circuit for an optical beam emitter.
In particular, the said step of transferring the said processed signal from the said moving station to the said fixed station comprises:
generating a magnetic field corresponding to the said processed signal at the said moving station in the direction of the said fixed station,
converting the said magnetic field to an electrical signal,
decoding the said electrical signal in such a way that the corresponding processed signal is obtained.
In a further aspect, the present invention relates to a wheel for vehicles, comprising a tyre fitted on a supporting rim, characterized in that it comprises
a moving station, located at a predetermined position on the said rim, capable of sending an optical beam towards the inner surface of the tyre, receiving the light reflected from the said surface and emitting a signal proportional to the deformations of the tyre in a longitudinal direction, in a transverse direction and in a vertical direction to a vehicle on which the said wheel is fitted,
a reflecting element positioned on the said inner surface of the tyre, comprising a region which has at least one area of high light reflection and one area of low light reflection, and which is capable of reflecting the said optical beam.